Diastereoselective aza MBH reaction

In the past years, only a few reports have dealt with a chiral auxiliary induced diastereoselective aza MBH reaction. In 1994, Kiindig et al. explored the reaction of methyl acrylate and acrylonitrile with enantiopure planar chiral o substituted Cr(CO)3. Under the catalysis of DABCO, the corresponding aza MBH adducts were obtained in good yields. Removal of the metal provided chiral amines in high yields and enantiomeric excesses [12]. Later on, Aggarwal ef al. used enantiopure Nsulfinimines in the aza MBH reaction with methyl acrylate in the presence of 3 hydroxyquinuclidine (3 HQD) and Lewis add. The desired adducts, functionalized P sulfonated amino acid derivatives, were obtained with good diastereoselectivities (Scheme 13.4) [13]. 

Recently, in the presence of an effective air stable nucleophilic trialkylphosphine organocatalyst, 1,3,5 triaza 1 phosphaadamantane (PTA), a chiral N thiophosphoryl imine bearing a (S) binaphthalene skeleton induced a diastereoselective aza MBH reaction that was carried out with fair chemical yields and moderate to excellent diastereoselectivities (up to >99% de) (Scheme 13.6) [15]. Removal of the chiral auxiliary provides the corresponding chiral amines in good yields. 

Also for the diastereoselective aza-MBH reaction (Scheme 7.10) between chiral A-thiophenyl imines and methyl vinyl ketone, PTA was found to be an active catalyst. The products were obtained in good yields (>80%) with excellent diastereoselectivities (>99% de, Ar = 4-F3CC6H4), albeit at long reaction times (up to 5 days) [52]. PTA is also an effective catalyst in the [3 + 2] cycloaddition of activated allenes with A-thiophosphoryl imines to give 3-pyrrolines [53]. 

Most recently, Xu et al. have demonstrated the first example of a diastereo-and enantioselective aza-MBH-type reaction by the asymmetric synthesis of p-nitro-y-enamines via a (li ,2i )-diaminocyclohexane thiourea derivative (182) mediated tandem Michael addition and aza-Henry reaction in good yields (up to 95%) with high enantioselectivities (up to 91% ee) and diastereoselectivities (up to 1 99 dr) (Scheme 2.90) easily prepared A -tosylimines and nitroalkene are employed as the starting materials. ... 

The diastereoselective aza-Morita-Baylis-Hillman reaction (aza-MBH) of chiral A -thiophosphoryl imines (60) with a,(3-unsaturated ketones have been reported by Zhou and co-workers. The corresponding aza-MBH adducts (61) were prepared in moderate chemical yields (64-75%) and in moderate ( 50% de) to excellent diastereoselect vities (>99% de) in the presence of an efficient, air-stable tri-azaphospha-adamantane organoca-talyst (62) (Scheme 20). 

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